The present invention relates to pin-type valve-gate bushings and nozzles for use with gas-assisted injection molding systems.
There are many processes and techniques today for a gas-assisted injection molding. Gas-assisted injection molding processes have added flexibility to the design and manufacture of plastic parts with their ability to produce partially hollow, lightweight, rigid parts with minimal sink marks and less tendency to warp. These processes can reduce material requirements, as well as equipment costs and cycle time, and thus have advantages over conventional injection molding processes and techniques for many applications.
In general, gas-assisted injection molding systems utilize gas, under pressure, to expand the plastic material in the mold and conform it to the mold cavity details. The gaseous fluid can be introduced into the mold in several ways, such as through a bushing, or machine nozzle in one or more cavities, or in more than one location. In conventional plastic injection molding processes, the molten plastic material is injected through sprue bushings, heated or unheated, into the cavities of hollow molds. Often, two or more sprue bushings attached to a common manifold are used. In this instance, the plastic melt coming from the injection molding machine through runners is distributed by a heated distributor block (or manifold) to the individual sprue bushings. One conventional method used to control the melt flow utilizes one or more pins or needle valves, also known as valve-gate bushings.
With these systems, a needle valve is inserted through the manifold into the sprue bushing and controlled for axial movement by a hydraulic, electric or pneumatic control device or mechanism. The needle valve has an elongated pin member which is moved axially by the control mechanism and is adapted to fit within an orifice in the end of the sprue bushing in order to open and close the passageway of plastic melt from the sprue bushing into the mold cavity. A second moveable pin member can be positioned inside the elongated pin member and, via a valve mechanism at the end of the two pin members, allow gas to enter the plastic in the mold cavity.
It is an object of the present invention to provide an improved valve-gate bushing or machine nozzle for use with a gas-assisted injection molding process. It is also an object of the present invention to provide an improved valve-gate bushing or nozzle with a moveable gate pin which is biased to its closed position and utilizes gas pressure to open the gas orifice and allow gas to flow into the plastic in the mold cavity.
The present invention provides an improved valve-gate type bushing or nozzle for use with gas-assisted systems, and fulfills the object and purposes noted above. The present invention provides a pin-type valve-gate device which easily and effectively opens and closes the flow of plastic material into the mold as desired, and also easily and effectively opens and closes the gas passageway into the mold cavity.
In particular, a moveable inner pin member is provided which cooperates with an outer pin member to open and close a gas passageway for passage of gas into the plastic material in the mold cavity. The inner pin member is biased by a spring washer or the like to its valve-close position. Upon entry of gas into the annular channel between the inner and outer pin members, the gas acts on a large surface of the inner pin member which overcomes the biasing force of the spring washer and opens the gas passageway to allow gas to enter into the mold cavity and plastic material. The ends of the outer and inner pin members mate with each other creating a valve or xe2x80x9cgatexe2x80x9d for entry of gas material into the mold cavity.
These and other objects, features, and benefits of the invention will become apparent from the following description of the invention, when taken together in view of the accompanying drawings and appended claims.